The present invention relates to a deflection yoke and a color cathode ray tube receiver using such a yoke, and more particularly to those equipped with a convergence corrector for correcting misconvergence of a color cathode ray tube employed in a television receiver, a display monitor or the like.
In a color cathode ray tube, a color picture is displayed on its screen by vertically and horizontally deflecting the forward directions of three electron beams emitted from an electron gun.
For deflection of electron beams, there is used a deflection yoke having a horizontal deflection coil and a vertical deflection coil.
In a cathode ray tube, a deflection yoke is installed in one region termed a cone which is defined from a neck of the tube to a funnel thereof.
A horizontal deflection current and a vertical deflection current are caused to flow, respectively, in a horizontal deflection coil and a vertical deflection coil on the orbits of three electron beams emitted from the electron gun, thereby forming deflection magnetic fields. The electron beams are deflected vertically and horizontally by such deflection magnetic fields.
In the color cathode ray tube, three electron beams emitted from its electron gun are converged on one point of a fluorescent screen via color selection electrodes of an aperture grill or a shadow mask, whereby a desired color picture is reproduced on the screen.
In this case, if there occurs misconvergence where the three electron beams fail to be converged on one point of the fluorescent screen, it causes some color deviation or color phase irregularity.
Generally, in any color cathode ray tube having an in-line type electron gun where a center electron beam G for lighting a green fluorescent layer and side electron beams R, B for lighting red and blue fluorescent layers are arranged in a line, misconvergence shown in FIG. 1 occurs on the screen when the vertical deflection magnetic field is a uniform one.
In this example, a red side beam R deviates leftward, while a blue side beam B deviates rightward.
It is widely known that this misconvergence can be corrected by forming the vertical deflection magnetic field into a barrel shape.
More specifically, there is generally performed a technique of adjusting the winding distribution of a vertical deflection coil to thereby form the vertical deflection magnetic field into a barrel shape .
However, if the vertical deflection magnetic field is formed into a barrel shape, there occurs another misconvergence in a vertical direction, as shown in FIG. 2A.
In case such vertical misconvergence is existent, the difference between the average value of the side beams R, B and the center beam G is termed VCR (Vertical Center Raster).
It is possible to achieve static correction of this VCR by means of adding, for example, some magnetic member to the electron gun.
Practically, however, the VCR is not always fixed in dimension, and there may arise some difference between the VCR at the t op and bottom of the screen along the Y-axis thereof, i.e., at the screen center, and the VCR at the horizontal top and bottom ends of the screen, i.e., at the screen corners.
For example, there may remain a pattern of FIG. 2B where the beam G is outside at the screen center, while the beam G is inside at the screen corners.
It is supposed here that the difference between the raster VCR at the screen center and the raster VCR at the screen corner is termed xcex94VCR.
In order to change such xcex94VCR, the following two measures may be adopted for example.
The first measure is carried out by adjusting the winding distribution of the vertical deflection coil to thereby balance the screen corner and the screen center.
The second measure is carried out by utilizing that a horizontal deflection magnetic field that affects the raster VCR at the screen corner.
More concretely, the screen corner and the screen center are balanced by adjusting the winding distribution of the horizontal deflection coil.
Now a consideration will be given below on the force exerted on the center beam G and the side beams R, B by the vertical deflection magnetic field in a barrel shape.
It is supposed that the magnetic fields exerted respectively on the in-line center beam G and side beams R, B are in the directions indicated by arrows in FIG. 3.
FIG. 3A shows an example where the electron beams are deflected upward along the Y-axis of the screen, and FIG. 3B shows another example where the electron beams are deflected toward the upper right end of the screen corner.
The horizontal component of the magnetic field exerted on each electron beam, i.e., the magnetic field for vertical deflection, can be changed by adjusting the winding distribution of the vertical deflection coil.
It is also possible to change the magnetic fields separately at the screen center and the screen corners to a certain extent.
However, if the horizontal component of the vertical deflection magnetic field is changed by adjusting the winding distribution of the vertical deflection coil, the vertical component of the vertical deflection magnetic field is also changed simultaneously therewith.
For this reason, if the winding distribution of the vertical deflection coil is altered, the horizontal convergence is affected as observed in the HCR (Horizontal Center Raster) which represents the difference between the average value of the side beams R, B and the center beam G.
Also in the case of adjustment by the winding distribution of the horizontal deflection coil, the concept is still the same although the direction of the magnetic field is different, and therefore it is possible to change xcex94VCR at the screen corner, but such adjustment affects the vertical convergence.
Further, any change of the magnetic fields affects the focus characteristics of electron beams as well as the convergence characteristics thereof.
Thus, in either of the first and second measures mentioned above, there exist some restrictions relative to the winding distribution in connection with the convergence or focus of the side beams R and B.
It is therefore difficult to optimize xcex94VCR by altering the winding distribution of the vertical deflection coil or the horizontal deflection coil.
The present invention has been accomplished in view of the problems described above. It is an object of the invention to provide a deflection yoke and a color cathode ray tube receiver using such a yoke equipped with a convergence corrector which is capable of correcting xcex94VCR independently to thereby achieve proper convergence with high precision.
According to one aspect of the present invention, there is provided a deflection yoke which comprises parabolic current producing means for producing a horizontal-period parabolic current and then supplying the parabolic current to a convergence correcting coil; sextuple-pole magnetic field generating means disposed around the orbits of three electron beams emitted from an electron gun, and exerting vertical force on the three electron beams by a sextuple-pole magnetic field generated in accordance with the horizontal-period parabolic current supplied from the parabolic current producing means; and saturable reactor means for modulating, by a vertical-period current, the horizontal-period parabolic current flowing in the sextuple-pole magnetic field generating means.
This deflection yoke is installed in a cone region of a cathode ray tube employed in a color cathode ray tube receiver.
In the deflection yoke having the above structure and a color cathode ray tube receiver using such deflection yoke, a horizontal-period parabolic current produced in the parabolic current producing means is caused to flow in the convergence correcting coil, so that any misconvergence is corrected by a correcting magnetic field generated by the convergence correcting coil.
The horizontal-period parabolic current is caused to flow also in the sextuple-pole magnetic field generating means.
Consequently, the sextuple-pole magnetic field generating means generates a sextuple-pole magnetic field in accordance with the horizontal-period parabolic current, and exerts vertical force on three electron beams by the sextuple-pole magnetic field.
In this case, the saturable reactor means modulates, by the vertical-period current, the horizontal-period parabolic current flowing in the sextuple-pole magnetic field generating means.
As a result, the horizontal-period parabolic current modulated at the vertical period is caused to flow in the sextuple-pole magnetic field generating means.
The above and other features and advantages of the present invention will become apparent from the following description which will be given with reference to the illustrative accompanying drawings.